This invention relates to a ring network comprising a plurality of nodes and to a method of collecting node information signals from the respective node stations in each node station.
A wide variety of ring networks have been proposed each of which comprises a plurality of nodes connected in a ring shape through a communication path, such as an optical path. Such ring networks have been disclosed in Japanese Unexamined Patent Publications Nos. 64-16,146 (16,146/1989), 64-89,636 (89,636/1989), and the like. In the ring networks disclosed in the above-references, communication among the nodes is made by the use of a token or by a polling operation. Such communication may be either unidirectional or bidirectional communication.
In addition, a synchronous optical network (SONET) transport system has been disclosed by Bellcore (Bell Communications Research) in TA-NWT-000253 and TR-TSY-000496 issued September 1990 and September 1991, respectively. In the TA-NWT-000253, generic operations requirements are defined in connection with the SONET transport system. On the other hand, generic criteria are described in the TR-TSY-000496 as regards SONET Add-Drop Multiplex Equipment which is operable in accordance with alarm surveillance requirements mentioned in the TR-TSY-000496.
At any rate, communication should be made among the nodes by indicating a destined node or nodes on transmitting information from a transmission one of the nodes. Let a specific one of the nodes collect or gather information transmitted from each of the nodes. In this event, the information should be often transmitted from each of the nodes to the specific node through an intermediate node or nodes allowing the information to pass therethrough.
Herein, it often happens that a fault takes place somewhere on the communication path in the SONET system and should be located in the SONET system by checking status information in the nodes one by one by a superintendent. Such checking and locating the fault is very troublesome, laborious, and time-consuming because the superintendent should go to positions at which the nodes are located and should thereafter check whether or not each of the nodes is normal.